1. Field of the Invention
The invention relates to sliding doors. More particularly, the invention relates to apparatus for reinforcing the sliding door of a pressure vessel.
2. Description of the Invention Background
Pressure vessels, such as industrial sterilizers and autoclaves, are well known in the art and are generally used in hospitals, industrial laboratories, and other facilities for the purpose of sterilizing various solid, porous, or liquid items.
Sliding doors are sometimes used in connection with such machines because they require a minimum of space in relation to the size of the opening they provide and they do not interfere with the loading and unloading of the machine. Sliding doors are held along opposing sides (vertical or horizontal, depending on the direction in which the door slides) by a retention system. The retention system of some conventional doors includes a rail or trough-like member in which the captive edge of the sliding door is received.
Because of the pressure forces which build up in pressure vessel chambers, sliding doors for these vessels must be generally designed to withstand large forces. Sliding pressure vessel doors, held captive on two sides, are subject to both a deflective and a stress force across the door surface. It has been observed that the forces acting on the door are relatively high at the door's center. Therefore, the cross-section of the door at its center must be sized to handle the increased forces in that area. Several conventional sliding doors use a flat plate door, uniform in cross-section. Others enhance the flat plate with reinforcing beams or channels.
The simplest conventional door design is one consisting of a thick metal plate, uniform in cross-section and machined for flatness. Manufacturing such a door does not involve welding, but is expensive and difficult because of the large mass of material required. The mill plate typically used does not have a flatness tolerance and, therefore, it is necessary to start with a thicker plate and machine it to the desired flatness and thickness. The flat plate must be thick enough to withstand the stresses at the door center. However, continuing this large cross-section out to the captive sliding edges of the door requires the use of a commensurately large width in the rail or trough of the door retention system. The width of the retention system is sometimes referred to as the gap. The larger gap in the door retention system required for a flat plate door in turn, provides a relatively long "tunnel" length for vessel loading and unloading from the interior to the exterior of the vessel.
One commercially available 26".times.26" pressure vessel door includes horizontal, reinforcing channel beam members which are intermittently welded to the surface of a flat plate member. The channel beam members are uniform in cross-section and extend across the full width of the door. The edges of the door are welded to large stiffener bars which ride within the trough of the door retention assembly. The width of the trough is relatively large to accommodate the large stiffener bars. Because of the size of the stiffener bars, this door also provides a relatively long "tunnel" length or loading and unloading.
A commercially available 17".times.18" door includes reinforcing beams in the form of bent angles in place of the channel beam members of the 26".times.26" door. Each bent angle reinforcing beam is also uniform in dimension across its span. The 17".times.18" door includes slider bars along both captive edges of the door. Each end of the bent angle reinforcing beams are joined to a stiffener bar. The slider bars which are received in the retention assembly, are not as thick as the stiffener bars of the 26".times.26" door so that the width of the trough in the retention system of the 17".times.18" door is smaller. However, this design requires a number of pieces and much welding. The bent angles do not reinforce the sliding surface or the engagement between the sliding surface with the door.
An additional concern which must be addressed in the design of sliding pressure vessel doors is that they include a properly supported sliding surface for door translation. The sliding surface must somehow be connected to the door edges such that the junction between the sliding surface and the door may withstand the high stress forces to which it is subjected.
It is therefore an object of the present invention to provide a pressure vessel closure and a means for reinforcing the closure that withstand the stress levels exerted across the door and at its edges while minimizing the width of the trough in the retention assemblies in which the door slides, thereby reducing "tunnel" length. The several different pressure vessel door designs which exist have not satisfactorily addressed these objectives.